Various packer seal designs have been tried to address potential leakage issues if the tubular interior wall is out of round. Large rubber rings with soft backups have been tried in the Premier packer line offered by Baker Hughes Incorporated. Another style that has an ability to compensate for out of roundness is an inflatable packer design although such designs are typically used in low pressure differential applications. Swelling packers can also take the irregular shape of the inside wall of a surrounding tubular but are generally felt as being more limited in the ability to withstand large pressure differentials. The ZXP line of packers from Baker Hughes Incorporated compensate for tubular out of roundness with very high setting forces so that the seal on the tight portions of the tubular with the intentions that portions of the seal will migrate to the looser portions of tubular where the radius has enlarged. This design has high pressure differential capability but the high setting force also presents a risk to the casing itself such as undue localized stress that can result in propagating a wall crack and potential tubular leakage.
What is needed and provided by the present invention is a compliant seal design and an associated seal setting system. The setting mechanism comprises a plurality of pistons about the packer mandrel at the outer periphery so that common applied hydraulic pressure advances all the pistons and selectively locks their movement for the set with a ratchet mechanism. Some of the pistons closest to where the tubular radius is greater then continue to apply force and axially displace portions of the seal assembly on an inclined surface for preferably plastic deformation in the axial direction that results in further radial extension so that the seal assembly seals all the way around in even significantly out of round tubulars. The pistons can be actuated to retract to overcome a locking effect from a ratchet lock ring and the seal assembly can be a simple rubber element with molded garter springs in place to assist in retraction or in the shape of a metal c-ring or scroll so that alone or in combination with a potential energy device such as a garter spring will pull the seal assembly to a smaller dimension for retrieval. The seal assembly is preferably a metallic housing with spaced flanges defining a groove in between where the seal material is disposed. A retrievable version of the seal assembly may or may not consist of a metallic housing. Minimizing the length of the seal assembly while providing backup to the seal element in both directions allows for use of reduced force to create the needed deformation for sealing in out of round tubulars. These and other features of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.